Installing braided brake lines and changing fluid

[omniflow]

Hi,

When installing braided brake lines at the same time as renewing the brake fluid, is it best to drain out the fluid before starting or keep as much fluid in the system as possible (using bungs?) and then make sure the fluid is renewed as part of the bleeding process? My assumption is drain it first - but I thought I'd ask on here anyway.

I'm planning on installing braided lines on all 4 corners, and I have 2 trolley jacks and 4 sturdy axle stands, so I should be able to get all 4 wheels off without a problem.

Thanks